Amplifiers with capacitor defined gain have advantages over resistor implemented amplifiers as capacitors do not introduce noise as resistors do nor do they introduce the self heating problem that resistors do. Capacitor implemented amplifiers are very stable and if the signal varies slowly e.g. 100 Hz there can be generally a naturally high input impedance. They are also easy to drive using lower current. One shortcoming of such devices is that they do not perform well at low and near d.c. frequencies. If a low frequency signal is introduced into a capacitor the current will be very small and easily overwhelmed by stray noise current. See A LOW-POWER LOW-NOISE CMOS AMPLIFIER FOR NEURAL RECORDING APPLICATIONS by Harrison et al., IEEE Journal of Solid State Circuits, Vol. 38, No. 6, June 2003, pages 958-965 incorporated herein in its entirety by this reference.